Attempting to create a new forum topic throws in the following error:

This page contains the following errors:

error on line 234 at column 43: Unescaped '<' not allowed in attributes values
Below is a rendering of the page up to the first error.

Moodle 2.3 (Build: 20120625), running locally on Apache 2.2.21 (Unix), MySQL 5.5.24, PHP 5.3.10.